KR20200072862A - Method for manufacturing negative electrode active material for rechargeable lithium battery, and rechargeable lithium battery including the same - Google Patents

Abstract

A method of manufacturing a negative electrode active material for a rechargeable lithium battery according to an embodiment of the present invention includes the steps of: manufacturing a mixture by mixing graphite and pitch; stirring the mixture at 500 to 2200 rpm, grinding graphite and coating pitch on the graphite surface; and carbonizing the pitch-coated graphite. The negative electrode active material for a rechargeable lithium battery has improved efficiency characteristics.

Description

A method for manufacturing a negative electrode active material for a lithium secondary battery, and a lithium secondary battery comprising the same TECHNICAL

A method for manufacturing a negative electrode active material for a lithium secondary battery, and a lithium secondary battery comprising the same.

Recently, lithium secondary batteries are rapidly evolving in the field of electronic communication devices such as tablet PCs and smartphones, and furthermore, as the field of application of electric vehicles expands, research and development efforts to increase energy storage capacity are gradually becoming concrete. At the same time, efforts are being made to increase the efficiency generated in the charging and discharging tasks of the anode material. Meanwhile, in recent years, the application of artificial graphite negative electrode materials having excellent output characteristics and life characteristics has been increasing. In particular, the trend of application of artificial graphite in the IT/mobile market and EV market is rapidly increasing. In the case of artificial graphite anode materials that are currently developed and commercialized, most of them use needle coke as a raw material. This is in the case of artificial graphite anode material produced using needle coke as a raw material, and has a capacity of 350 to 360 mAh/g. The efficiency varies depending on the electrolyte conditions, but most products generally reach 92 to 93%.

In the case of the artificial graphite anode material, a carbon coating process is mostly applied to the surface to increase the output characteristics. In general, soft carbon is coated on the graphite surface, and it is common to show a tendency for capacity and efficiency to decrease as the carbon content increases in this process. The reason is that the capacity and efficiency of the coating material Soft Carbon compared to the capacity of graphite is relatively low.

As a method of reducing the carbon content in the coating process, a method of increasing the coating uniformity by smoothing the surface of the negative electrode material or applying a liquid coating process is currently being applied. Graphite-based anode materials, especially artificial graphite anode materials, are composed of secondary particles in which primary particles that are sharper than natural graphite are assembled. Therefore, it is characterized by a very rough particle surface. As a process for smoothing the surface of the anode material, a process of rotating in a high-speed blade mill, finely pulverizing the angular portion of the surface of the anode material, and removing the generated fine powder through an air flow classification process is applied. In general, this process is called a grinding process (Particle Grinding). When this grinding process is performed, when coating amorphous carbon on a graphite surface, the graphite particle surface becomes smooth, so that the coating uniformity is relatively increased, thereby reducing the carbon coating amount. However, as the damage to the graphite particles increases as it goes through the grinding process, the specific surface area of the graphite particles increases and the disadvantages of decreasing the yield through the process of removing the graphite fine powder by air flow classification are pointed out.

In order to solve this problem, a technique for coating amorphous carbon with an inorganic carbon and an inorganic surface has been proposed. However, a pitch is used as an amorphous carbon precursor, and a liquid coating process using an organic solvent is selected. The liquid coating has an advantage in that it is possible to secure the uniformity of the carbon coating layer on the surface of the negative electrode material. However, in that it uses an organic solvent, there are problems such as increase in process cost and occurrence of environmental problems. In addition, in the case of using hydrophobic inorganic materials, there is a disadvantage that a purification process using an acid or an alkali must be introduced to control the uncoated content. Also, although a technique of applying a dry coating process is known, a method for coating a relatively large amount is proposed, and efficiency characteristics need to be improved.

Provided is a method for manufacturing a negative electrode active material for a lithium secondary battery, and a lithium secondary battery comprising the same. Specifically, a method of manufacturing a negative electrode active material for a lithium secondary battery with improved efficiency characteristics, and a lithium secondary battery comprising the same are provided.

A method of manufacturing a negative electrode active material for a lithium secondary battery according to an embodiment of the present invention comprises the steps of preparing a mixture by mixing graphite and pitch; Stirring the mixture at 500 to 2200 rpm, coating the crushed graphite and the pitch on the graphite surface; And carbonizing the pitch-coated graphite.

In the step of preparing the mixture, the D50 particle diameter of graphite may be 10 to 30 μm.

In the step of preparing the mixture, 1 to 5 parts by weight of pitch may be mixed with respect to 100 parts by weight of graphite.

In the step of preparing the mixture, the specific surface area of graphite may be 1 to 4 m ² /g.

The steps of grinding the graphite and coating the pitch on the graphite surface may be performed for 10 minutes to 3 hours.

After the grinding of graphite and the step of coating the pitch on the graphite surface, the graphite coated with the pitch may have a specific surface area of 2 to 3.1 m ² /g.

With respect to the specific surface area (A) of graphite before the step of coating the crushed graphite and the graphite surface, after the step of coating the crushed graphite and the graphite surface with the pitch, the specific surface area of the graphite coated with the pitch (B) The ratio (B/A) may be 80% or less.

The carbonizing step may be carbonized at a temperature of 700 to 1300°C in a non-oxidizing atmosphere.

A lithium secondary battery according to an embodiment of the present invention includes a positive electrode; cathode; And an electrolyte, and the negative electrode includes a negative electrode active material for a lithium secondary battery manufactured by the above-described method.

The negative electrode active material for a lithium secondary battery manufactured through the manufacturing method according to an embodiment of the present invention simultaneously performs the grinding process and the coating process, thereby increasing the yield compared to the graphite particles produced through the grinding process and performing a general dry coating process. Compared to the carbon-coated graphite particles produced, the particle surface becomes smoother, so the efficiency characteristics are improved.

1 is a schematic flowchart of a method of manufacturing a negative electrode active material for a lithium secondary battery according to an embodiment of the present invention.
2 is a scanning electron microscope (SEM) photograph of particles after the carbonization step in Example 1.
3 is a scanning electron microscope (SEM) photograph of particles after the carbonization step in Example 2.
4 is a scanning electron microscope (SEM) photograph of particles after the carbonization step in Example 3.
5 is a scanning electron microscope (SEM) photograph of graphite particles in Comparative Example 1.
6 is a scanning electron microscope (SEM) photograph of particles after the carbonization step in Comparative Example 2.

Terms such as first, second and third are used to describe various parts, components, regions, layers and/or sections, but are not limited thereto. These terms are only used to distinguish one part, component, region, layer or section from another part, component, region, layer or section. Accordingly, a first portion, component, region, layer or section described below may be referred to as a second portion, component, region, layer or section without departing from the scope of the present invention.

The terminology used herein is only to refer to a specific embodiment and is not intended to limit the invention. The singular forms used herein also include plural forms unless the phrases clearly indicate the opposite. As used herein, the meaning of “comprising” embodies a particular property, region, integer, step, action, element, and/or component, and the presence or presence of other properties, regions, integers, steps, action, element, and/or component. It does not exclude addition.

Although not defined differently, all terms including technical terms and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present invention pertains. Commonly used dictionary-defined terms are further interpreted as having meanings consistent with related technical documents and currently disclosed contents, and are not interpreted as ideal or very formal meanings unless defined.

In addition, in the present specification, the D50 particle size means a particle size when particles having various particle sizes are accumulated up to 50% by volume.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art to which the present invention pertains can easily practice. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.

1 schematically shows a flowchart of a method of manufacturing a negative electrode active material for a lithium secondary battery according to an embodiment of the present invention. The flow chart of the method of manufacturing the negative electrode active material for a lithium secondary battery of FIG. 1 is merely for illustrating the present invention, and the present invention is not limited thereto. Therefore, a method of manufacturing a negative electrode active material for a lithium secondary battery can be variously modified.

As shown in Figure 1, a method of manufacturing a negative electrode active material for a lithium secondary battery comprises the steps of preparing a mixture by mixing graphite and pitch (S10); Stirring the mixture at 500 to 2200 rpm, coating the pitch on the graphite ground and the graphite surface (S20); And carbonizing the pitch-coated graphite (S30). In addition, if necessary, a method of manufacturing a negative electrode active material for a lithium secondary battery may further include other steps.

First, in step (S10), a mixture is prepared by mixing graphite and pitch.

In one embodiment of the present invention, graphite may be used without particular limitation. Specifically, natural graphite or artificial graphite may be used as the graphite. More specifically, artificial graphite subjected to granulation and graphitization using coke as a raw material may be used.

The D50 particle diameter of graphite may be 10 to 30 μm. When using graphite having an appropriate D50 particle size, efficiency characteristics may be further improved.

In the step of preparing the mixture, 1 to 5 parts by weight of pitch may be mixed with respect to 100 parts by weight of graphite. In one embodiment of the present invention, since the pitch is coated together with the grinding, even if a small amount of the pitch is coated, the specific surface area of graphite can be effectively reduced.

In preparing the mixture, the specific surface area of graphite may be 1 to 4 m ² /g. More specifically, it may be 1.5 to 3.5 m ² /g. More specifically, it may be 3 to 3.5 m ² /g.

Next, in step (S20), the mixture is stirred at 500 to 2200 rpm, to coat the grinding of graphite and the pitch on the graphite surface.

In step (S20), the phenomenon of the grinding of graphite and the coating of the pitch on the graphite surface occurs simultaneously. Specifically, in step (S20), by operating the coating equipment in the form of a blade mill at an appropriate speed, it is possible to coat the pitch on the graphite surface at the same time as grinding the graphite.

Grinding is a process of smoothing graphite particles, and means pulverizing the square portion of the graphite particles. In the case of a general grinding process, the fine powder generated in the grinding process is removed through an air flow classification process, but in one embodiment of the present invention, since the pitch is coated on the graphite surface together with the grinding, there is no need to remove the fine powder separately. Therefore, it is possible to prevent the yield from being reduced by grinding.

When coating the pitch on the grinding surface of graphite and the graphite surface, the mixture can be stirred at 500 to 2200 rpm. When the stirring speed is too small, the coating may not be made uniformly, and grinding may not be performed properly. When the stirring speed is too fast, the impact on the graphite particles is large, and rather, the specific surface area of the graphite particles may increase. Therefore, it is possible to stir at the speed in the above-mentioned range. More specifically, the mixture may be stirred at 1000 to 2200 rpm. More specifically, it can be stirred at 1300 to 2200rpm. More specifically, it can be stirred at 1800 to 2100rpm.

Step S20 may be performed for 10 minutes to 3 hours. If the time is too short, grinding and coating may not be performed properly. Even if the time is longer, a more uniform coating cannot be expected, but rather, an impact applied to graphite accumulates and a specific surface area of graphite particles may increase. More specifically, step S20 may be performed for 30 minutes to 2 hours.

After the grinding of graphite and the step of coating the pitch on the graphite surface, the graphite coated with the pitch may have a specific surface area of 2 to 3.1 m ² /g. As such, the specific surface area of graphite is reduced through grinding and coating, so that efficiency characteristics can be improved. More specifically, the pitch-coated graphite may have a specific surface area of 2.2 to 3.0 m ² /g. More specifically, the pitch-coated graphite may have a specific surface area of 2.4 to 2.8 m ² /g. More specifically, the pitch-coated graphite may have a specific surface area of 2.5 to 2.7 m ² /g.

With respect to the specific surface area (A) of graphite before the step of coating the crushed graphite and the graphite surface, after the step of coating the crushed graphite and the graphite surface with the pitch, the specific surface area of the graphite coated with the pitch (B) The ratio (B/A) may be 80% or less.

Next, in step S30, the pitch-coated graphite is carbonized.

In one embodiment of the present invention, the carbonization process removes volatiles and induces pyrolysis, solidification and conversion to carbonaceous material. The carbonization step may be performed at a temperature of 700 to 1300°C. The atmosphere gas may be a non-oxidizing gas, and may be performed in a nitrogen or argon atmosphere. The carbonizing step may be performed for 30 minutes to 5 hours. More specifically, it may be 1200 to 1300 ℃.

The negative electrode active material for a lithium secondary battery manufactured through an embodiment of the present invention has a small specific surface area, and thus has excellent discharge capacity and initial charge/discharge efficiency. In addition, the 3C/0.1C discharge capacity ratio is also excellent. Specifically, the discharge capacity may be 351mAh/g or more. The initial charge/discharge efficiency may be 91.1% or more. The 3C/0.1C discharge capacity ratio may be 81% or more.

In another embodiment of the present invention, the anode; cathode; And an electrolyte, wherein the negative electrode provides a lithium secondary battery including a negative electrode active material prepared by the above-described method.

Specifically, the electrolyte is at least one selected from the group containing fluoro ethylene carbonate (fluoro ethylene carbonate, FEC), vinylene carbonate (VC), ethylene sulfonate (ES), and combinations thereof It may be to further include the above electrolyte additives.

The negative electrode active material and thus the characteristics of the lithium secondary battery are as described above. In addition, the battery configuration other than the negative electrode active material is generally known. Therefore, detailed description will be omitted.

Hereinafter, preferred examples of the present invention, comparative examples prepared against the same, and evaluation examples thereof will be described. However, the following examples are only preferred examples of the present invention, and the present invention is not limited to the following examples.

Example 1

As artificial graphite, artificial graphite having a particle size of 353 mAh/g and a particle size (d50) of 15 µm was prepared. The specific surface area (BET) was 3.3 m ² /g.

Artificial graphite and petroleum-based pitch (ZL 250) were mixed for 30 minutes using a roll mill under a weight ratio of 100:3.

The mixture was put into a coating facility (Mechano Fusion, Hosokawa Co.) and operated at a constant speed for 1 hour. The driving speed was changed to the speed summarized in Table 1 below, and grinding and coating were performed. The specific surface area after grinding and coating was summarized in Table 1 below.

Then, the powder was carbonized by maintaining it at 1000°C for 1 hour in a nitrogen atmosphere.

Example 2

The same procedure as in Example 1 was carried out, but the operation speed was changed to the speed summarized in Table 1 below.

Example 3

The same procedure as in Example 1 was carried out, but the operation speed was changed to the speed summarized in Table 1 below.

Comparative Example 1

Carbonization was carried out in the same manner as in Example 1, without mixing with the pitch.

Comparative Example 2

It was carried out in the same manner as in Example 1, but was carried out by changing the operating speed to 2300 rpm, summarized in Table 1 below.

Graphite: Pitch weight ratio Coating speed (RPM) Specific surface area
(m ² /g) Example 1 100: 3 1000 3.0 Example 2 100: 3 1500 2.8 Example 3 100: 3 2000 2.6 Comparative Example 1 100: 0 - 3.3 Comparative Example 2 100: 3 2300 3.5

After the grinding and coating steps in Examples 1 to 3 and Comparative Example 1, scanning electron microscopy (SEM) pictures of particles are shown. Examples 1 to 3 can be confirmed that the surface is smooth compared to the comparative example. Among Examples 1 to 3, it can be seen that Example 3 formed the smoothest surface. In the case of Comparative Example 2, when it was operated at a condition of more than 2000 rpm, that is, 2300 rpm, the tendency for the particles to become smooth increased, but the tendency for BET to increase as small protrusions on the particle surface increased. This is considered to be due to the fact that the damage of graphite particles increases rather than under excessive coating speed conditions.

Experimental Example-Fabrication of lithium secondary battery (Half-cell) and initial discharge capacity and efficiency measurement

Electrodes were prepared using the negative electrode active materials prepared in Examples 1 to 3 and Comparative Examples, a binder (Carboxy Methyl Cellulose (CMC) and Styrene Butadiene Rubber (SBR)), and a conductive material (Denka Black). The negative electrode active material: conductive material: CMC: SBR was mixed so that the weight ratio was 95.6:1:1.1:2.3.

After coating the Cu current collector so that the electrode loading amount was 10 g/cm 2 and the electrode density was 1.6 g/cc, it was rolled, and a CR2032 type coin half cell was prepared.

As the electrolyte, a composition product of EC: EMC = 1: 1 (1.0M LiPF6) in which VC (Vinyl Carbonate) was mixed at 0.5 wt% was used.

Li Metal was used as the anode for the evaluation of the cathode.

0.1C, 5mV, 0.005C cut-off charging and 0.1C 1.5V cut-off discharge proceeds three times under the initial activation (Activation) conditions, and after activation, 0.1C, 5mV, 0.005C cut-off charging and 0.1C , 1.5V cut-off discharge conditions were measured for charging and discharging capacity under high power conditions. As described above, the current during charging and discharging was measured at 0.1C in the initial 3 cycles and 3C in the subsequent 4th cycle.

Discharge capacity under the above conditions, initial discharge and efficiency, and the ratio of the discharge capacity at 3C to the initial discharge capacity at 0.1C are summarized in Table 2 below.

Discharge capacity (mAh/g) Initial charge/discharge efficiency (%) 3C/0.1C discharge capacity
ratio(%) Example 1 353 91.2 81 Example 2 351 91.8 83 Example 3 352 93.4 88 Comparative Example 1 351.6 91.0 80 Comparative Example 2 351.1 90.8 85

As can be seen in Table 2, it can be seen that Examples 1 to 3 have improved discharge efficiency compared to Comparative Example 1 while maintaining a similar level. In addition, when looking at the ratio of 3C/0.1C, which is an index indicating the output characteristics, it can be confirmed that the specific surface area is the most reduced and the best output characteristics are obtained in the case of Example 3 in which the surface is smoothly controlled. In the case of, the discharge capacity and the ratio of 3C/0.1C are similar to the examples, but it can be confirmed that the initial efficiency characteristics are significantly deteriorated.

The present invention is not limited to the above embodiments, but may be manufactured in various different forms, and those skilled in the art to which the present invention pertains have other specific forms without changing the technical spirit or essential features of the present invention. It will be understood that can be carried out. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

Claims (9)

Preparing a mixture by mixing graphite and pitch;
Agitating the mixture at 500 to 2200 rpm, coating the crushed graphite and the pitch on the graphite surface; And
Method for producing a negative electrode active material for a lithium secondary battery comprising the step of carbonizing the pitch-coated graphite. According to claim 1,
In the step of manufacturing the mixture, the D50 particle size of graphite is 10 to 30㎛ method for producing a negative electrode active material for a lithium secondary battery. According to claim 1,
In the step of preparing the mixture, a method for producing a negative electrode active material for a lithium secondary battery, mixing 1 to 5 parts by weight of pitch with respect to 100 parts by weight of graphite. According to claim 1,
In the step of preparing the mixture, the specific surface area of graphite is 1 to 4 m ² /g method for producing a negative electrode active material for a lithium secondary battery. According to claim 1,
The method of manufacturing a negative electrode active material for a lithium secondary battery is performed for 10 minutes to 3 hours in the step of coating the crushed graphite and the pitch on the graphite surface. According to claim 1,
After the step of coating the crushed graphite and the graphite surface, the pitch-coated graphite has a specific surface area of 2 to 3.1 m ² /g. According to claim 1,
With respect to the specific surface area of graphite before the step of coating the crushed graphite and the pitch on the graphite surface,
After the step of coating the crushed graphite and the graphite surface, the ratio of the specific surface area of the graphite coated with the pitch is 80% or less. According to claim 1,
The carbonizing step is a method of manufacturing a negative electrode active material for a lithium secondary battery carbonized at a temperature of 700 to 1300°C in a non-oxidizing atmosphere. anode; cathode; And an electrolyte;
The negative electrode is a lithium secondary battery comprising a negative electrode active material for a lithium secondary battery produced by the method according to any one of claims 1 to 8.

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